vi] Rusts 69 
stem. In very bad attacks the grain may become 
shrivelled. 
In cases of attacks by some of the fungi which live 
alternately on two hosts it is possible to reduce the 
amount of damage by the removal of one of the host 
plants. In the case of Puccinia graminis this plan does 
not succeed. In Australia there are no barberry bushes 
and no plant has been found on which the aecidium 
stage occurs and yet this fungus survives and does 
considerable damage. This is also true of certain 
parts of England. In this case it is supposed that the 
uredospores live until the next season’s crop is growing 
and then infect it. It is possible that the mycoplasm 
hypothesis put forward by Eriksson in which he states 
“that the germ of the rust is present in the seed of the 
host plant” may have some foundation, but it is not 
usually accepted. This fungus has several different 
varieties which all appear the same under the micro- 
scope, but each will only infect certain host plants. 
That usually found on oats will not attack wheat or 
barley. That found on wheat, however, is occasionally 
found on oats and barley. 
From our point of view the Puccinia graminis 
attacking our cereals may be divided into three different 
varieties: (a) usually attacks wheat and occasionally 
barley, oats and rye; (b) usually attacks barley, rye, 
couch grass, and other grasses, but does not attack 
wheat and oats; (c) usually attacks oats, tall oat 
grass, and cocksfoot, but not wheat, barley or rye. 
There are other varieties which attack grasses but 
do not attack cereals. 
